Under certain operating conditions aircraft are vulnerable to accumulation of ice on component surfaces. If left unchecked, such accumulations can eventually so laden the aircraft with additional weight and so alter the airfoil configuration of the wings as to cause undesirable flying conditions. A wide variety of systems have been purposed for removing ice from aircraft during flight or for preventing its accumulation on the leading edge surfaces of such aircraft. These systems can be categorized in three ways: thermal, chemical and mechanical.
The mechanical category of deicing systems covers a wide range of devices, all of which distort the airfoil surface in some manner so as to shed ice from the airfoil surface. A subcategory of mechanical deicing systems are electro-expulsive deicers wherein electric current is passed in opposite directions through a pair of conductors located closely to one another so that interacting magnetic fields force the conductors apart to thereby deform the ice collecting walls. An example of electro-expulsive deicing systems can be found in three disclosures discussed hereinafter.
In U.S. Pat. No. 3,809,341 to Levin et al., flat buses are arranged opposite one another with one side of each bus being adjacent an inner or obverse surface of an ice collecting wall. An electric current is passed through each bus and the resulting interacting magnetic fields force the buses apart and deform the ice collecting walls. The disadvantage of this system is that each bus operates on the structural skin of the airfoil and a predetermined skin deflection is required to provide a set level of ice removal, thereby necessitating large force requirements in order to generate the needed amount of skin deflection. Such high skin deflections are believed likely to cause fatigue in the skin.
U.S. Pat. No. 4,690,353 to Haslim et al. discloses a system wherein one or more overlapped flexible ribbon conductors are embedded in an elastomeric material affixed to the outer surface of an airfoil structure. The conductors are fed large current pulses and the resulting interacting magnetic fields produce an electro-expulsive force which distends the elastomeric member and separates the elastomeric member from a solid body such as ice thereon. The conductors in a single conductive layer as disclosed by Haslim et al. have a serpentine or zig-zag configuration.
Commonly owned U.S. Pat. No. 4,875,644 to Adams et al. discloses an electro-expulsive deicing system wherein a plurality of expulsive elements are placed in different layers on the airfoil surface, with each element being comprised of electrically conductive members interconnected such that electric current flowing in the conductive members flows in the same direction in adjacent electrically conductive members in a first sheet-like array and also flows in adjacent electrically conductive members of a second sheet-like array in a direction opposite to the first.
The present invention is an improvement over the electro-expulsive deicing systems disclosed in Haslim et al. and Adams et al.. Applicants have found that disposition of multiple electro-expulsive elements within a common, metal clad, attachable boot provides improved deicing characteristics.